Electric machines, such as motors and generators, typically include a stator that is mounted inside a housing and a rotor that is supported for rotation relative to the stator. Electric machines are often integrated into devices such as appliances. The size and/or capacity of the device incorporating the electric machine may be an important factor in the purchasing decision. The size and power of the electric machine also has a significant impact on the overall size and capacity, respectively, of the device.
The power density of an electric machine is defined as the ratio of the power output and the volume of electric machine. A relatively high power density (e.g., high power output relative to volume) is usually desirable. The high power density allows the electric machine to have either a smaller overall size for a given power output or a higher output for a given size.
When the electric machine rotates during operation, the electric machine vibrates, which produces noise. The noise level of the electric machine may be an important factor in the buying decision. Therefore, it is desirable to decrease vibration, which reduces noise. Conventional approaches for reducing vibration tend to decrease power density as well. In other words, reduced vibration and noise has been achieved at the cost of reduced power output and/or increased volume.